Copier `_subdirectory` allows template root escape via parent-directory traversal

{
  "id": "501af0e9d1e2d19a12506b9d9a9426d67ec59867526248c58174a2dd18ed6679",
  "url": "https://osv.dev/vulnerability/CVE-2026-34726",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Copier `_subdirectory` allows template root escape via parent-directory traversal",
    "summary": "Copier is a library and CLI app for rendering project templates. Prior to version 9.14.1, Copier's _subdirectory setting is documented as the subdirectory to use as the template root. However, the current implementation accepts parent-directory traversal such as .. and uses it directly when selecting the template root. As a result, a template can escape its own directory and make Copier render files from the parent directory without --UNSAFE. This issue has been patched in version 9.14.1.",
    "evidence": "osv:CVE-2026-34726",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-34726",
      "aliases": [
        "CVE-2026-34726",
        "GHSA-85v3-4m8g-hrh6",
        "PYSEC-2026-2134"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/copier-org/copier",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "f6ac94689a0a672ae1a53d442740fb85dbd4004f"
                },
                {
                  "fixed": "cb80a3ffc9c3787de3ed837e04ca29a0ff8ca3df"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:copier-org:copier:*:*:*:*:*:python:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "9.14.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "cb80a3ffc9c3787de3ed837e04ca29a0ff8ca3df"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "f6ac94689a0a672ae1a53d442740fb85dbd4004f"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v9.14.1"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v9.14.0",
            "v9.13.1",
            "v9.13.0",
            "v9.12.0",
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            "v5.1.0",
            "v5.0.0",
            "v4.1.0",
            "v4.0.2",
            "v4.0.1",
            "v4.0.0",
            "v3.2.0",
            "v3.1.0",
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            "v3.0.0-alpha4",
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            "v3.0.0-alpha1",
            "v2.5.1",
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            "v2.4.2",
            "v2.4.1",
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            "v2.2.3",
            "1.1.1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-34726.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:49.985438569Z",
      "provider": "osv",
      "references": [
        "https://github.com/copier-org/copier/releases/tag/v9.14.1",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34726.json",
        "https://github.com/copier-org/copier/security/advisories/GHSA-85v3-4m8g-hrh6",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-34726",
        "https://github.com/copier-org/copier/commit/cb80a3ffc9c3787de3ed837e04ca29a0ff8ca3df"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-22"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34726.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-34726",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 518309,
  "published_at": "2026-04-02T18:07:35.517+00:00"
}